In packet data systems according to the Third Generation Partnership Project (3GPP) standard, comprising in particular the General Packet Radio Service (GPRS) and its derivatives, Quality of Service (QoS) mechanisms are used for requesting and guaranteeing certain Quality of Service (QoS) criteria for packet data connections, i.e. Packet Data Protocol (PDP) contexts. One example of such a QoS criterion is the bit rate of a connection, but also other QoS parameters that are defined in 3GPP standards may be used.
The bit rate that can be supported by the packet data system is dependent on capabilities of both the mobile station and the network. One of the main limiting factors is the mobile station's multislot class, which indicates the number of Packet Data Channels (PDCHs) that a mobile station can handle (in a GPRS system, this multi-slot class ranges from 1 to 8). Obviously, applications in a mobile station demanding a certain QoS can request only a bit rate that is less or equal to the maximum bit rate supported by the mobile station's multislot class. The network then decides on a Guaranteed Bit Rate (GBR) according to the mobile station's capabilities, but uses also some other network related parameters in said decision, e.g. the network load.
The Dual Transfer Mode (DTM) enables simultaneous Circuit-Switched (CS) and Packet-Switched (PS) connections in mobile radio networks. Basically this means that part of the air interface capabilities of the mobile station are being allocated from pure PS usage also for CS channels. Consequently, the maximum available bit rate for PS connections is lower during DTM activity than during PS-only activity. Since PDP contexts, i.e. packet data connections with a related QoS, are normally reserved for a long time, DTM activity in parallel needs to be taken into account in some way when QoS parameters are requested by a mobile station and guaranteed by the network.
According to 3GPP standards, currently CS connections are prioritised over PS connections during parallel connection set-up (DTM mode establishment). This means also that the applications operating on PS connections and relying on previously negotiated QoS for said PS connections can suffer dramatically from parallel CS connections, because the bit rate of the PS connections may significantly fall below the guaranteed bit rate when parallel CS connections are prioritised, and said applications running on top of said PS connections then may no longer properly function.
Furthermore, when a CS connection is added to already established PS connections, the resources of the mobile station such as processing power and memory limits may be exceeded without control, thus affecting both the PS and CS connections and the applications using said connections.